ASoC: cs42l56: Fix stereo channel register assignment for Headphone and LineOut volume mixers

Stereo Headphone and LineOut volume mixers are now attached to HPA+HPB, LOA+LOB.

Reported-by: Ryan Harvey <ryan.harvey@cirrus.com>
Signed-off-by: Ryan Harvey <ryan.harvey@cirrus.com>
Signed-off-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@linaro.org>